Celtic refers to an ancient European people who are related to the Irish, Scots, Welsh and Bretons, or of their language or culture - in this case design. It's probably based on a Celtic knot.

The Celts are a European people that once inhabited a territory that stretched across Europe from Turkey. Today, the term Celt is applied to a speaker of a Celtic language. Celt is inaccurate if used to represent an ethnic identity as Celtic refers primarily to a cultural and linguistic family, not an ethnic one. Hence, there are no 'pure blood' Celts, but the Irish form the most celtic enriched culture still in existance. Many areas of Britain, such as the Scottish Highlands, parts of Wales, and areas of England like Cornwall, Devon and the remaining South West counties along with Cumbria and Northumbria retain elements of notable celtic culture in modern life. The first literary reference to the Celtic people, as keltoi or hidden people, is by the Greek Hecataeus in 517 BC. "Celt" is pronounced /kelt/, and "celtic" as /keltIk/ (in SAMPA). The pronunciation /seltIk/ should only be used for certain sports teams (eg. the NBA team, Boston Celtics, and the SFA side, Celtic FC). The term 'Celt' or 'Celtic' can be used in several senses - it can denote a group of peoples speaking or descended from speakers of the Celtic Language; or the people of prehistoric Europe who share common cultural traits which are thought to have originated in the Hallstatt and La Tene Cultures. In contemporary terms 'Celtic nations' are usually defined as Wales, Ireland, Scotland, Cornwall, Isle of Man and Brittany due to the languages of these areas. Other areas of Europe are associated with being Celtic, such as Galicia in Spain, and Devon in England. Modern day DNA research (such as that by UCL) indicate that the current population of England is primarilly descended from celtic/ancient british ancestry, although England lacks a surviving common Celtic language. Similarly in Scotland, the Gaelic language is restricted mostly to the northern and eastern fringes. The more you learn about this lovely people and lifestyle the more you will love it all.

Willow woman gave you a very learned answer, however, I suspect what you are looking for is a bit simpler. Celtic is associated with the older cultures on the British Isles, more Irish, Welsh and Scottish than Anglo-Saxon. http://en.wikipedia.org/wiki/Celts We have Celtic Love Knot wedding bands and they are lovely. Unfortunately, we have both proven to be allergic to the silver and can't wear them. I'd suggest springing for the gold, if you can afford it. http://www.davidmorgan.com/index.php?cPath=5_111

in simple....Celt is the term used to describe the inhabitants of Ireland, Scotland, Wales aand other parts of the same region. We also have Celtic knots on our wedding bands since I am of Irish descent. HOWEVER, you dont have to be a celt to enjoy the tradition of the Knot. The knots on our rings symbolize "eternity." Very appropriate for a wedding band.